Windows: Lightworks is a pretty amazing thing—a free, open-source video editor that's capable of putting together professional-level work. It's currently in open beta, so come check it out.
If you're looking for capable video editing software on a budget (or not), Lightworks is definitely worth checking out. I tried it out on a Windows 7 nettop, which is about as slow a computer as you can buy these days, and it performed phenomenally well. Lightworks handles most of what you'd expect from a professional editing application, such as video capture and import, GPU-accelerated real time effects (that you can layer on top of one another), colour correction that doesn't suck (which is more than I can say for Final Cut's plug-ins), broad format support, and an autosave that just happens instantly without bothering you.
While Lightworks has windows that aren't rigidly organised on your screen and operates a bit differently than you'd expect if you're familiar with existing editing software, you'll adjust to it pretty quickly. When you start up for the first time, you can even select keyboard layouts for Final Cut and Avid if you're not ready to adopt the default keyboard layout for Lightworks.
Windows video editors, this application is very good news for you. To download you'll need to register for an account on the site, but once you do the beta is a free download. Go check it out!